IEuro-American Post-Graduation Program in
Health (PEPGS)  Doctorate in Physiology Nuestra Senõra de la Asunción
Catholic University (UC) ParaguayIILaboratory of Biosciences of the Human
Motricity (LABIMH)  Federal University of Rio de Janeiro State (UNIRIO) 
BrazilIIIAugusto Motta University (UNISUAM) 
BrazilIVState University of Londrina (UEL) 
BrazilVLaboratory of Prognostic
Aspects of Intervention and Care in Health and Human Performance 
Western Universiy of Santa Catarina (UNOESC)  BrazilVIStricto Sensu Post-Graduation Program in Nursing and Biosciences (PPgEnfBio  Doctorate) of
the Federal University of Rio de Janeiro State (UNIRIO)  Brazil

Training, both performed with high-performance athletes and
aiming health, includes besides aerobic resistance,
localized muscular resistance, flexibility and strength1. Thus,
to know the mutual interrelations between these physical qualities, even in
acute level, would boost the training efficiency. In the specific case of the
interrelation results of flexibility training in the
quality of strength is still little known2,3.

In order to develop flexibility, training can be divided in a
maximal way (flexibilizing)4 or a submaximal way (stretching). When
the aim is to develop flexibility, the maximum intensity is suggested and among
the training methods, we highlight the static flexibilizing (passive method)5.
This method aims the development of the range of motion beyond the normal
threshold, and has as quantitative parameters of application the duration and
frequency of the remaining time in the many articular movements6.

The static flexibilizing method regularly applied has been
suitable for the development of flexibility4,7. However, chronic
studies which aim to check its influence on the strength levels are scarce.

In order to characterize whether the performed exercise is
stretching or flexibilizing, some intensity control techniques are used8.
Among the control techniques, biomarkers which detect body alterations to the
application of physical exertions can be verified. They mainly serve as a
controlling agent of the physical stress level to which the individual is being
submitted.

Specifically to
the control of muscular stress, hydroxyproline (HP) is one of the biomarkers
used to measure the level of intensity to which the muscle has been submitted9,10.
Thus, increase in the hydroxyproline levels in the urine indicates collagen
catabolism of the locomotor system. On the other hand, lower post-exercise
levels characterize lower level of microinjury on the mentioned system11-13.

Therefore, in the trial to fill in the
information gap presented, the study had the aim to verify whether maximal
flexibility intensity training (flexibilizing) would be
able to cause statistically significant improvement in the neuromuscular
parameters (static maximal strength levels and flexibility level), as well as
in the hydroxyproline concentration in the urine, in young adults, after 12
weeks of intervention.

METHODS

The sample analyzed in this study was
randomly obtained from the universe of 500 EPCAR students, and was composed of
70 male individuals, cadets of the groups of the Preparatory School of Air
Cadets (EPCAR), physically active and aged between 15 and 19 years old. The
following exclusion criteria were adopted for sample definition: to b athletes
or sedentary; to present any visually perceived pathology, declare or detected
in the initial medical examination; not to have frequency equal or above 85% in
the training sessions and/or not be volunteers in the research.

The cadets were randomly divided by a simple
draw, in two groups: experimental group of static flexibilizing (FG, n = 35)
and control group (CG, n = 35) (table 1).

All volunteers have signed the Free and
Clarified Consent Form according the declaration of Helsinki14 and
the Resolution 196/96 of the National Health Board15. The study was
submitted to and approved by the Ethics in research Committee of the
Euro-American Chain /RJ under the number 05/2009.

Instruments and procedures

At the first moment, preliminary procedures
were performed in which body mass and stature measurements were collected and
relative fat was calculated by the protocol of three skinfolds16,
respectively, with a Filizola digital scale with resolution of 100g, model
PL150 Personal
Line, (Brazil, 1999); a Sanny professional
stadiometer (Brazil) and a Lange skinfold caliper (USA), with 1mm of resolution
and steady pressure of 10g/mm2. All collection points followed the
guidelines from the International
Standards for Anthropometric Assessment17.

Maximal isometric strength (MIS) was measured
by the 1RM protocol of static contraction19, through a multiuse
digital dynamometer, with load cell for PC, developed by the Center of Sports
Physiology Study (CEFISE), which has resolution of 0.1kgf or 1N, total capacity
of 250kgf or 2,500N and precision of 1% of total capacity. It works with data
acquisition system N2000 PRO. Three movements were observed: shoulder
horizontal flexion (SHF), shoulder horizontal extension (SHE) and lumbar spine
extension (LSE).

Its application took place after detailed
orientation, in which the participants were asked to apply maximum strength as
fast as possible in a single try. Both flexibility and strength were measured
in consecutive days, always at the same time, applied by the same experienced
evaluators. The temperatures were similar in both days with approximate values
of 25ºC. Moreover, the participants were instructed not to perform any type of
vigorous activity during the 24 hours preceding the test.

The damage produced in the muscular collagen
by the work performed was measured by a laboratory examination in the urinary
excretion, according to the Nordin method20, which identified the
concentration of the biochemical marker hydroxyproline according to the HPROLI
2h protocol21.

The individuals participating in the research
were told by the pharmacist in charge not to ingest any kind of ergogenic,
nutritional or pharmacological substances, besides physiological resources or
alcohol during the period of the study and in the 48 hours to the study. An
eating record of 24 hours before the examination was hence performed. In that
record, it was tried to verify whether the participants had ingested diet
without the presence of red or white meat, clam, sweets, ice-cream or gelatin,
in order to control and standardize the dietetical intake of HP.

The subjects were submitted to a 12-hour fast
(night shift) for performance of the sample and, immediately after having
eliminated the first urine, were hydrated with water. From that moment on,
during a two-hour period, from seven to nine 'o clock, the urine collection was
performed in the sterile plastic containers, identified and previously
distributed, all provided by the São Lucas Laboratory, in Barbacena, whose
quality certification is pointed by the ISO 9001/2000 record. The containers
were immediately stored in ice and transported to the São Lucas Laboratory,
Belo Horizonte, under the partnership with the Lab Chain for analysis.

Urinary HP concentration was determined with the kit ClinRep® (complete kit for
hydroxyproline in urine) through the colorimetric
method. In that method, the HP is oxidized with pyrrole, followed by coupling with paradimethylaminobenzaldehyde. The
reagents are prepared in
house, namely: buffering solution (pH 6.0),
chloramine solution T reactive by Erlich, standard solution for hidroxyproline,
phenolphthalein, sodium hydroxy, isopropanol and perchloric acid.

The samples were analyzed in the HPLC system
containing a gradient pump, an injecting valve, a heat column (60ºC), an UV/VIS
detector for 472nm, a computer with the HPCL software and a hand regulator.

The intervention occurred during 12 weeks, in
a frequency of four times per week, at the end of the warm-up of the regular
physical education class of the institution, always at the same time (at
16:00h). Experimental training of the following maximum arches of the articular
movements was performed: shoulder joint horizontal extension (SHE), shoulder
joint horizontal flexion (SHF) and lumbar spine flexion (LSF).

Intensity of the exertion applied during the
exercises was controlled with the use of the perceived exertion scale (PERFLEX)22 in all training sessions. After the application of the respective training
programs, all the cadets participating in the study were released to continue
the mandatory program expected in the physical education sessions, which during
the intervention period was composed only of aerobic activities.

The flexibilizing group (FG) performed the
experimental training in pairs through three sets of static flexibilizing
exercises until the discomfort threshold (subjective pain sensation)23,
remaining in that position for six seconds. After that, through a light
flexion, it reached the highest movement arch possible and remained in that
position for 10 extra seconds4,7. The exertion intensity reached the
discomfort range between levels 61 and 80 of the PERFLEX (X = 69.2 ± 7.5),
characterizing the maximum intensity. The results were calculated by the final
mean of all intervention daily means.

It is worth mentioning that for control of
the inactivity of the control group (CG), they participated in the weekly
meetings.

At the end of the intervention period, all
tests of diagnostic evaluation were reapplied.

Statistical treatment

The statistical program SPSS 14.0 for Windows
was used for data analysis. Descriptive statistics methods were applied, in
which data are presented in mean, standard deviation, minimum and maximal
values. Normality of variables was confirmed by the Kolmogorov-Smirnov test.
Analysis of variance (ANOVA) with repeated measures in the time and group
factors, followed by Tukey post-hoc test, was used to identify the possible differences in the intra
and intergroup comparisons. The p < 0.05 value was adopted for
statistical significance.

RESULTS

The intra and intergroup results of the
static fexibilizing application, during 12 weeks in young adults, may be
observed concerning the neuromuscular parameters evaluated in figures 1, 2 and 3.

The results presented in figure 1 represent
the pre and post absolute values for the variables concerning flexibility. In
the intragroup analysis, significant improvement for the SHF (∆% = 3.9%;
p = 0.001), SHE (∆% = 21.1%; p = 0.001) and LSF (∆% = 73.8%; p =
0.001) movements of the FG group can be observed. The CG movements did
not present significant differences.

When the differences obtained after the
intervention period are compared, it can be observed that the intergroup
results represent the gains of the FG being significantly higher than the gains
observed in the CG for all movements, where we have: SHF (p-value= 0.018), SHE
(p-value = 0.004) and LSF (p-value = 0.001).

In figure 2 it is possible to observe the pre
and post absolute values for the strength levels. The results demonstrate, for
the intragroup analysis, significant improvement for the SHF (∆% = 20.4%;
p = 0.001) and LSE (∆% = 4.0%; p = 0.008) movements of the experimental
group (FG).

The intergroup analysis presents that when
the levels of percentage improvement are compared, the gains observed by the FG
are significantly higher than the gains observed by the CG for the SHF (p-value
= 0.001) and LSE (p-value = 0.004) movements.

Figure 3 presents the results of the pre and
post absolute values for the hydroxyproline levels in the urine. The intragroup
results demonstrated decrease; not significant though in CG and FFG. When the
intergroup decrease was compared, significant difference have not been verified
between them.

The data analysis denotes that the power of
the observed experiment was of 86% for a beta calculated of
0.14.

DISCUSSION

The results of
the comparison of the alterations in the neuromuscular parameters demonstrated
significant increase of the static maximum strength levels and the flexibility
level, associated with the decrease of the variability level of the
hydroxyproline values in the urine, in favor of the intervention of the static
flexibilizing.

The improvement in the flexibility level and
strength levels obtained through the intervention of static flexibilizing have
also been observed in another study24, in which flexibility training
through the static flexibilizing method was promoted, in 38 university
students, during 10 weeks. The authors verified significant improvement for all
assessed variables, among which flexibility and strength.

In flexibility, the improvement values obtained by Kokkonen et al.24 were lower than the ones found in the present study. Considering that the training method in
both studies was similar, this difference probably occurred caused by the
intervention time of the experiment and the number of weekly sessions used by
Kokkonen et
al.24 being
smaller than the one used in the preset study.

Maximum strength was evaluated in the knee
flexion and extension movements. The results demonstrated significant increase
of 15.3% for the flexion movement and of 32.4% for the extension movement.
These results, in a comparative analysis with the present study, evidence great
similarity between these studies. Both have proved improvement in the maximum
strength levels with the chronic intervention of the training by the static method;
however, there is difference in the evaluation protocol applied and in the
evaluated joints.

Our study is also similar to another 25 performed with Brazilian university students where 30 individuals aged between
18 and 39 years, among which 11 were men, performed a flexibilizing program
during six weeks. The results revealed significant gains in flexibility and in
the peak torque angle of the thigh posterior musculature and the knee flexors
and extensors. These results are similar to the present study, although the
evaluated joint, the sample used and the methodological procedures are
different.

The evidenced improvement of muscular
strength was also verified in an investigation26 with static
flexibilizing exercises and FNP, during 15 days, in 19 volunteers. The results
reported increase in the isokinetic maximum volunteer torque, both in the
eccentric moment and the concentric moment. However, the flexibility
effects were not evaluated. The authors concluded that the
evaluated methods were able to improve muscular performance.

The proposal to verify the flexibility
training effects was also performed in rats. Published results present increase
of exercised muscle mass after four and three weeks of intervention27, 28.
This fact suggests that the increase of the strength level would be associated
with increase of muscle mass.

In order to justify this hypothesis, it is
worth mentioning a study29 in which 30 minutes of daily stretching
were sufficient to cause increase in the number of sarcomeres in series.
Coutinho et
al.28 went
beyond and reported that, after the three weeks of stretching for 40 minutes,
increase of 5% in length and of 4% in the number of sarcomeres in series could
be observed.

Flexibility improvement could be corroborated in other chronic
research. One study30 which compared the chronic
effects of the static and ballistic flexibilizing methods during six weeks, in
81 healthy subjects, mean age of 27.1 ± 4.4 years, divided in three groups,
where one of them was the control group, when comparing the effects caused by
the respective methods, verified significant increase of range of motion of the
ankle in the two experimental groups. It is worth mentioning that this study is
different from ours, since other joints and much shorter intervention time were
used (approximately half).

Another study31 which also
verified improvement in the flexibility levels after an intervention period was
conducted in 69 older women aged between 60 and 70 years, during 24 weeks. The
authors compared the chronic effect of the static flexibilizing and stretching.
The results demonstrated percentage mean of improvement for the flexibilizing
of 95.4%, much higher than the one observed in our study and in the literature
in general. However, it should be considered that the intervention time and the
sample may have significantly contributed to this difference.

The results of the flexibility can also be
compared with the study by Conceição et al.4 also performed with the Brazilian Air Force cadets. The authors
conducted an investigation methodologically very similar to the present study,
only being different concerning the time of duration of the intervention period.
Contrary to the present study, which lasted 12 weeks, they compared after eight
training weeks, the effect of different permanence times in the static
flexibilizing. Therefore, 49 male young adults, also EPCAR cadets, divided in
four sample subgroups, aged between 15 and 19 years were used. The results of
the study indicated that all groups presented significant flexibility gains and
that 10 seconds is a sufficiently efficient time for this increase. These
results corroborate the ones verified in the present study, in which
significant improvement of the flexibility levels was also found after use of
10 seconds of permanence in the static flexibilizing.

Voigt et
al.7 also performed a study
methodologically similar to ours. The authors verified that
the flexibility behavior of 59 men, mean age of 23.7 ± 3.6 years, submitted to
a single repetition of 10 seconds of duration of the static flexibilizing
method. Although the intervention time of the study (16 weeks) is longer than
the one used in ours (12 weeks), in both studies the number of work sessions
was 48. In the research carried out by Voigt et al.7 three weekly sessions were performed, while the present one
performed four weekly session. The results demonstrated in both studies
significant increase of the articular amplitude in all the evaluated movements.

The HP levels obtained through the static
flexibilizing intervention, did not demonstrate significant differences, despite having been smaller. However, due to the
decrease of the variance of the HP levels, improvement in the physical fitness
is observed, since the HP represents a correlation with muscular injuries
derived from the muscular stress. These findings still need further
investigation to be deeper and better discussed, since in their vast majority,
the studies investigate about the acute effects of HP.

Nevertheless, Caetano et al.13 performed a chronic study of the HP
levels in eight male military police officers, members of the corporation from
the Rio de Janeiro state, aged between 25 and 45 years and patients of the
General Hospital of the Military Police and with acute low back pain. They
verified the effects of mixed stretching in 10 hydrokinesiotherapy sessions, on
the urinary HP levels and on pain. Contrary to the present study, the results
by Caetano et
al.13 demonstrated significant decrease of HP, despite the fact the police officers
have performed lower work volume. Probably, this result is explained by the
pain scenario f the officers. Since they had acute low back pain, their HP
levels would be increased and, after the treatment with hydrokinesiotherapy,
the injury of the muscle tissue would have also significantly reduced, as well
as the HP levels in the urine.

Considering the results obtained and
presented in this study, as well as its limitations, we can conclude that the
flexibilizing practice during a long period may cause besides significant
increase of flexibility, significant improvement of the static maximum strength
levels, as well as decrease in the level of variability of the hydroxyproline
values in the urine. However, it is crucial that the issue under consideration
is further investigated in detail. The amount of studies concerning the use of
the flexibility training for development of strength is still too small. Future
researchers should verify if other flexibility methods are also able to promote
such adaptation.